1. Field of the Invention
The present invention relates to a device for measuring ion activity for the quantitative analysis of a specific ion activity (or ion concentration) contained in an aqueous liquid, particularly a body fluid such as blood, urine or saliva by utilizing potentiometry.
2. Description of Prior Art
There have been known methods for measuring specific ion activity contained in a liquid sample (e.g., tap water, river water, sewage or industrial drainage) or a body fluid (e.g., blood, urine or saliva) by using an ion activity mesuring device in the form of a sheet.
In these methods, a reference liquid and a liquid sample are spotted onto the surface of the ion-selective membrane of each of a pair of ion-selective electrode sheets which are electrically insulated from each other, and then a potential difference between the ion-selective electrodes is measured under such conditions that both liquids are electrically connected to each other through a bridge, to thereby determine the ion activity of the liquid sample.
Examples of such ion activity measuring devices employable in these methods, are described, for instance, in Japanese Patent Provisional Publication Nos. 52(1977)-142586, 56(1981)-6148 and 58(1983)-211648.
In these devices, a pair of ion-selective electrode sheets are arranged in such a manner that ion-selective membranes are positioned on the upper side, and on the ion-selective membranes are provided with liquid receiving openings (openings for introducing a reference liquid and a liquid sample). In practically determining the ion activity by the use of these devices, the reference liquid and the liquid sample are spotted on the ion-selective membranes through the liquid receiving openings by using a pipet, etc. and a potential difference between both ion-selective electrodes is measured to thereby determine ion activity. There is also known a device comprising plural pairs of ion-selective electrodes, which can determine ion activity of plural kinds of ions by only once-spotting of a reference liquid and a liquid sample thereonto. Such a device is disclosed in Japanese Patent Provisional Publication No. 58(1983)-211648.
Though the above-described method using plural pairs of the ion-selective electrodes for determining ion activity of several kinds of ions simultaneously is simple and advantageous, it has been found that the method has the following disadvantages.
When a bandage, a flax net, a lawn, a silk gauze or a filter paper is used s a porous liquid distributing member, said method has a problem in that in the measurement of ion activity, particularly potassium ion activity in whole blood, diluted whole blood solution or a blood sample containing blood cells (particularly, erythrocyte), the blood sample suffers hemolysis in the ion activity measuring device and as a result, the measured value of potassium ion activity is often deviated from true potassium ion activity in the blood sample and does not coincide with potassium ion activity in plasma or serum obtained by removing blood cells from the same blood sample.
When a gauze is used as a porous liquid distributing member, hemolysis is inhibited to a large extent, but it is easily deformed and has much difficulty in cutting it into a given length. When a cloth composed of a synthetic polymer fiber such as a polyester fiber is used, whole blood hardly suffers hemolysis, but the spreading of the liquid is very slow.
Therefore, these materials are not satisfactorily employable as a liquid distributing member for the abovedescribed ion activity measuring device which enables ion activity of several kinds of ions to be simultaneously measured by only one device.